The present invention relates to calculators capable of converting values expressed in any one of a plurality of variably related units to any other one of the plurality of such related units.
The development of the hand-held and desk top calculator has expanded the horizons for performing a variety of calculations easily and relatively inexpensively. The variety of such calculators in existence, the rapidity of change and the increase in the capability of these calculators is too well known to require comment. Not only has the capability of such calculators increased at what seems like an exponential rate, but the cost to the consumer has decreased almost as rapidly.
One type of calculator that has become very popular, at least in the United States, is one having the capability to provide conversion between the English or U.S. system of measurement and the metric system. Typically, a single key stroke provides conversions between two specific units, e.g., between inches and millimeters, feet and meters, gallons and liters, pounds and killograms, .degree. F and .degree. C and others. A variety of calculators with this capability exist, such as the Hewlett Packard Model HP-55.
In spite of the convenience of such calculators stemming from this type of conversion capability, there are limitations because each conversion is limited to two specific units. In addition, metric and other similar conversions involve fixed relationships. Clearly, any type of conversion problem in which the factors may not remain constant could not suitably utilize this approach.
One clear example of this type of problem is in the field of international finance which involves almost continuous conversion from one currency to another. Since the value of currencies relative to each other vary from day to day, the rigid type of conversion techniques described above cannot be used.
Even those calculators which are designed to provide more flexibility in conversions by allowing the user to select the base from which the conversions are to be made are limited to this capability. One more flexible conversion approach, the Rockwell A4521MOS-LSI calculator circuit, allows the selection of the base unit from which conversions are to be made and permits English-metric conversions from a selected base unit to a number of other related units of length, including area volume, fluid, mass and temperature units. This approach is still limited in that it provides preset fixed relationship conversions from a selected unit within a system to some other units within that system. Since this calculator is limited to conversion between preselected units having a fixed relationship, the number of units available for conversion is usually limited, and multiple conversions between units having a varying relationship to each other is not possible.